1. Field of the Invention
The invention relates to methods and apparatus for reversibly coupling rotating shafts.
2. Coupling Tools to High-Speed Motors
Many types of rotary tools are preferably coupled to a driving shaft with a safe and reliable coupler which is also reversible (allowing for the rapid removal of a tool from the coupling and/or the coupling of one tool in place of another to a driving shaft). Applications in which there are particularly stringent safety and reliability requirements for couplers include the drilling, grinding, polishing and related material-removal operations which are inherent in many medical and dental treatment plans. Rotary tools (e.g., drills, burs, grinding wheels and cutting wheels) reversibly coupled to high-speed motors can precisely shape tooth, bone, or biocompatible implant material during certain surgical procedures. Such shaping operations often require precise tool positioning and as many as thirty tool changes in the course of a single operation. Thus, each rotating tool shaft would preferably be lockable securely into its coupler (i.e., substantially preventing its accidental disconnection from the coupler), but the lock would preferably be easily and surely reversed to allow tool insertion or removal or tool changes.
Surgical applications of a tool shaft coupler include a requirement to keep the total time under anesthesia as short as possible for each patient. Thus, connecting and disconnecting tools via a reversibly locking tool shaft coupler should preferably be quick and simple, even for a person wearing surgical gloves. Required motions to lock or unlock the connector, or to insert or remove a tool should be relatively uncomplicated. Further, because tools may reach rotational speeds in excess of 20,000 revolutions per minute, positive (and separate) indications would preferably be provided to clearly signify to a human operator either improper placement of a tool shaft within a coupler or inoperability of a coupler shaft lock. Moreover, once connected, a tool shaft and tool shaft coupler should not be subject to accidental unlocking (which could allow disconnection of the tool), either due to operator error or mechanical failure. Thus, a tool shaft coupler lock release mechanism would preferably comprise a separate coupler unlocking component which would be required to release the lock but which would normally be removed before the motor applies torque to the tool. Accidental failure of the operator to remove the unlocking component should not, however, pose a safety hazard during relatively brief operation of the motor. Further, accidental application of motor power to a tool shaft coupler during changing of a tool should not result in driving shaft rotation before the tool is securely locked in the coupler.
Tool shaft couplers should be capable of transmitting axial forces (i.e., tension or compression forces acting substantially parallel to the tool shaft longitudinal axis) alone or in combination with torque (i.e., rotational forces acting substantially about the tool shaft longitudinal axis). All such forces should be effectively transmitted, i.e., without substantial axial displacement of the tool shaft with respect to the driving shaft, without substantial rotational slippage of the driving shaft with respect to the tool shaft, and without substantial distortion of the driving shaft, tool shaft or coupler. Any tool shaft coupling failure leading to shaft displacement, distortion or slippage could lead to whipping of the tool shaft, tool overheating and/or tool shaft breakage. In turn, any of these events could lead to accidental uncoupling of the tool shaft from the driving shaft, leading to a risk of patient injury and possible difficulty in removing a damaged tool shaft from a coupler. These problems would be particularly acute in coupler and tool designs wherein both torque and axial forces are transmitted by substantially identical tool shaft surfaces. Hence, improved tool shaft couplers and mating tool shafts would comprise surfaces used to transmit torque which would preferably be different from those used to transmit axial forces. Even more preferably, at least some surfaces transmitting torque and axial forces would preferably be spaced apart to avoid or reduce potentially damaging stress concentrations within a tool shaft and/or driving shaft.